Wafer dividing method

ABSTRACT

A method of dividing, along dividing lines, a wafer having function elements formed in areas sectioned by the dividing lines formed in a lattice pattern on the front surface, comprising: a frame holding step for affixing the back surface of the wafer to a dicing tape mounted on an annular frame; a deteriorated layer forming step for forming a deteriorated layer along the dividing lines in the inside of the wafer by applying a pulse laser beam capable of passing through the wafer to the wafer along the dividing lines, from the side of the front surface of the wafer held on the frame; a dividing step for dividing the wafer into individual chips along the dividing lines by exerting external force along the dividing lines where the deteriorated layers have been formed of the wafer held on the frame; an expansion step for enlarging the interval between chips by stretching the dicing tape affixed to the wafer divided into individual chips; and a picking up step for picking up each chip from the expanded dicing tape.

FIELD OF THE INVENTION

The present invention relates to a wafer dividing method comprisingdividing, along dividing lines, a wafer having function elements formedin areas sectioned by the dividing lines formed in a lattice pattern onthe front surface, and picking up the obtained individual chips.

DESCRIPTION OF THE PRIOR ART

In the production process of a semiconductor device, a plurality ofareas are sectioned by dividing lines called “streets” arranged in alattice pattern on the front surface of a substantially disk-likesemiconductor wafer, and a circuit (function element) such as IC or LSIis formed in each of the sectioned areas. Individual semiconductor chipsare manufactured by cutting the semiconductor wafer along the dividinglines to divide it into the areas having a circuit formed therein. Anoptical device wafer comprising light-sensitive elements (functionelements) such as photodiodes or light-emitting elements (functionelements) such as laser diodes laminated on the front surface of asapphire substrate is also cut along dividing lines to be divided intoindividual optical devices such as photodiodes or laser diodes, andthese optical devices are widely used in electric equipment.

Cutting along the dividing lines of the above semiconductor wafer oroptical device wafer is generally carried out by using a cutting machinecalled “dicer”. This cutting machine comprises a chuck table for holdinga workpiece such as a semiconductor wafer or optical device wafer, acutting means for cutting the workpiece held on the chuck table, and acutting-feed means for moving the chuck table and the cutting meansrelative to each other. The cutting means includes a spindle unit thatcomprises a rotary spindle, a cutting blade mounted on the spindle and arotary drive mechanism for driving the rotary spindle. The cutting bladecomprises a disk-like base and an annular cutting edge, which is mountedon the side wall peripheral portion of the base and formed as thick asabout 20 μm by fixing diamond abrasive grains having a diameter of about3 μm to the base by electroforming.

Since the cutting blade has a thickness of about 20 μm, the dividinglines for sectioning chips must have a width of about 50 μm and hence,the area ratio of the dividing lines to the wafer is large, therebyreducing productivity. Further, since a sapphire substrate, siliconcarbide substrate and the like have high Mohs hardness, cutting with theabove cutting blade is not always easy.

As a means of dividing a plate-like workpiece such as a semiconductorwafer, a laser processing method for applying a pulse laser beam capableof passing through the workpiece with its focusing point set to theinside of the area to be divided is also attempted nowadays. In thedividing method making use of this laser processing technique, theworkpiece is divided by applying a pulse laser beam having an infraredrange capable of passing through the workpiece with its focusing pointset to the inside to the workpiece, from one surface side of theworkpiece to continuously form a deteriorated layer along the dividinglines in the inside of the workpiece and exerting external force alongthe dividing lines whose strength has been reduced by the formation ofthe deteriorated layers. This method is disclosed by Japanese Patent No.3408805, for example.

Although a process for dividing the wafer into individual chips bycompletely cutting it with the above cutting machine and picking up thechips has been established, a production line making use of thistechnique is not established yet and its development is under waythrough trial and error because a technique for forming a deterioratedlayer along the dividing lines in the inside of the wafer by using apulse laser beam cannot divide the wafer perfectly.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a wafer dividingmethod capable of establishing a process comprising the steps of forminga deteriorated layer along dividing lines in the inside of a wafer byusing a pulse laser beam, dividing the wafer into individual chips alongthe deteriorated layers and picking up the chips.

To attain the above object, according to the present invention, there isprovided a method of dividing, along dividing lines, a wafer havingfunction elements formed in areas sectioned by the dividing lines formedin a lattice pattern on the front surface, comprising:

-   -   a frame holding step for affixing the back surface of the wafer        to a dicing tape mounted on an annular frame;    -   a deteriorated layer forming step for forming a deteriorated        layer along the dividing lines in the inside of the wafer by        applying a pulse laser beam capable of passing through the wafer        to the wafer along the dividing lines, from the side of the        front surface of the wafer held on the frame;    -   a dividing step for dividing the wafer into individual chips        along the dividing lines by exerting external force along the        dividing lines where the deteriorated layers have been formed of        the wafer held on the frame;    -   an expansion step for enlarging the interval between chips by        stretching the dicing tape affixed to the wafer divided into        individual chips; and    -   a picking up step for picking up each chip from the expanded        dicing tape.

Preferably, the deteriorated layers formed in the inside of the wafer inthe deteriorated layer forming step are exposed to at least the backsurface of the wafer.

Preferably, the above dividing step is carried out by stretching thedicing tape in the expansion step.

Since the wafer dividing method of the present invention comprises theabove steps, it is possible to establish a process comprising the stepsof forming the deteriorated layer along the dividing lines in the insideof the wafer by applying a pulse laser beam capable of passing throughthe wafer having function elements in the areas sectioned by thedividing lines formed on the front surface in a lattice pattern to thewafer along the dividing lines, dividing the wafer into individual chipsalong the deteriorated layers and picking up the chips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a semiconductor wafer to be divided bythe wafer dividing method of the present invention;

FIG. 2 is a perspective view showing a state where a back surface of thesemiconductor wafer shown in FIG. 1 is affixed to a dicing tape mountedon an annular frame;

FIG. 3 is a perspective view of the principal section of a laser beamprocessing machine for carrying out the deteriorated layer forming stepin the wafer dividing method of the present invention;

FIG. 4 is a block diagram schematically showing the constitution of thelaser beam application means provided in the laser beam processingmachine shown in FIG. 3;

FIG. 5 is a schematic diagram for explaining the focusing spot diameterof a pulse laser beam;

FIGS. 6( a) and 6(b) are diagrams for explaining the deteriorated layerforming step in the wafer dividing method of the present invention;

FIG. 7 is a diagram showing a state where deteriorated layers are formedin the inside of the wafer in the deteriorated layer forming step shownin FIGS. 6( a) and 6(b);

FIG. 8 is a diagram showing a first embodiment of the dividing step inthe wafer dividing method of the present invention;

FIG. 9 is a diagram showing a second embodiment of the dividing step inthe wafer dividing method of the present invention;

FIG. 10 is a diagram showing a third embodiment of the dividing step inthe wafer dividing method of the present invention;

FIG. 11 is a diagram showing a fourth embodiment of the dividing step inthe wafer dividing method of the present invention;

FIG. 12 is a perspective view of a pick-up device for carrying out theexpansion step and the pick-up step in the wafer dividing method of thepresent invention;

FIGS. 13( a) and 13(b) are diagrams showing the expansion step in thewafer dividing method of the present invention;

FIGS. 14( a) and 14(b) are diagrams showing the dividing step and theexpansion step, which are carried out using the pick-up device shown inFIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail hereinunder with reference to the accompanying drawings.

FIG. 1 is a perspective view of a semiconductor wafer as a wafer to bedivided according to the present invention. The semiconductor wafer 2shown in FIG. 1 is a silicon wafer having a plurality of dividing lines21 formed in a lattice pattern on the front surface 2 a, and circuits 22are formed as function elements in a plurality of areas sectioned by theplurality of dividing lines 21. The front surface 2 a of the thusconstituted semiconductor wafer 2 is polished to a predeterminedthickness.

The back surface 2 b of the above-described semiconductor wafer 2 isheld on a dicing tape mounted to an annular frame (frame holding step).In this frame holding step, as shown in FIG. 2, the back surface 2 b ofthe semiconductor wafer 2 is put on the surface of the extensible dicingtape 30 mounted on the annular frame 3. The above dicing tape 30 ismanufactured by coating acrylic resin paste to the surface of a 100μm-thick sheet substrate made of polyvinyl chloride (PVC) to a coatingthickness of about 5 μm in the illustrated embodiment. This paste hasthe property of reducing its adhesive force by an external stimulus suchas ultraviolet radiation.

After the above-described frame holding step, there comes the step offorming a deteriorated layer along the dividing lines in the inside ofthe wafer by applying a pulse laser beam capable of passing through thewafer to the wafer along the dividing lines from the front surface 2 aside of the semiconductor wafer 2. This deteriorated layer forming stepis carried out by using a laser beam processing machine 4 shown in FIGS.3 to 5. The laser beam processing machine 4 shown in FIGS. 3 to 5comprises a chuck table 41 for holding a workpiece, a laser beamapplication means 42 for applying a laser beam to the workpiece held onthe chuck table 41 and an image pick-up means 43 for picking up an imageof the workpiece held on the chuck table 41. The chuck table 41 is soconstituted as to suction-hold the workpiece and moved in aprocessing-feed direction indicated by an arrow X and an indexing-feeddirection indicated by an arrow Y in FIG. 3 by a moving mechanism thatis not shown.

The above laser beam application means 42 has a cylindrical casing 421arranged substantially horizontally. In the casing 421, as shown in FIG.4, a pulse laser beam oscillation means 422 and a transmission opticalsystem 423 are installed. The pulse laser beam oscillation means 422comprises a pulse laser beam oscillator 422 a composed of a YAG laseroscillator or YVO4 laser oscillator and a repetition frequency settingmeans 422 b connected to the pulse laser beam oscillator 422 a. Thetransmission optical system 423 comprises suitable optical elements suchas a beam splitter, etc. A condenser 424 housing condensing lenses (notshown) constituted by a set of lenses that may have a known formation isattached to the end of the above casing 421. A laser beam oscillatedfrom the above pulse laser beam oscillation means 422 reaches thecondenser 424 through the transmission optical system 423 and is appliedfrom the condenser 424 to the workpiece held on the above chuck table 41at a predetermined focusing spot diameter D. This focusing spot diameterD is defined by the expression D (μm)=4×λ×f/(π×W) (wherein λ is thewavelength (μm) of the pulse laser beam, W is the diameter (mm) of thepulse laser beam applied to an objective lens 424 a, and f is thefocusing distance (mm) of the objective lens 424 a) when the pulse laserbeam having a Gauss distribution is applied through the objectivecondenser lens 424 a of the condenser 424 as shown in FIG. 5.

The image pick-up means 43 mounted onto the end of the casing 421constituting the above laser beam application means 42 is constituted byan infrared illuminating means for applying infrared radiation to theworkpiece, an optical system for capturing infrared radiation applied bythe infrared illuminating means, and an image pick-up device (infraredCCD) for outputting an electric signal corresponding to infraredradiation captured by the optical system, in addition to an ordinaryimage pick-up device (CCD) for picking up an image with visibleradiation in the illustrated embodiment. An image signal is transmittedto a control means that will be described hereinafter.

The deteriorated layer forming step which is carried out by using theabove laser beam processing machine 4 will be described with referenceto FIG. 3, FIGS. 6( a) and 6(b) and FIG. 7.

In this deteriorated layer forming step, the dicing tape 30 side of thesemiconductor wafer 2 is first placed on the chuck table 41 of the laserbeam processing machine 4 shown in FIG. 3 (therefore, the front surface2 a of the semiconductor wafer 2 faces up), and the semiconductor wafer2 is suction-held on the chuck table 41 by a suction means that is notshown. In FIG. 3, FIGS. 6( a) and 6(b) and FIG. 7, the annular frame 3mounting the dicing tape 30 is omitted but it is supported by thesuitable clamp mechanism of the chuck table 41. The chuck table 41suction-holding the semiconductor wafer 2 is brought to a position rightbelow the image pick-up means 43 by a moving mechanism that is notshown.

After the chuck table 41 is positioned right below the image pick-upmeans 43, alignment work for detecting the area to be processed of thesemiconductor wafer 2 is carried out by using the image pick-up means 43and the control means that is not shown. That is, the image pick-upmeans 43 and the control means (not shown) carry out image processingsuch as pattern matching, etc., to align a dividing line 21 formed in apredetermined direction of the semiconductor wafer 2 with the condenser424 of the laser beam application means 42 for applying a laser beamalong the dividing line 21, thereby performing the alignment of a laserbeam application position. The alignment of the laser beam applicationposition is also carried out on dividing lines 21 that is formed on thesemiconductor wafer 2 and extend in a direction perpendicular to theabove predetermined direction.

After the dividing line 21 formed on the semiconductor wafer 2 held onthe chuck table 41 is detected and the alignment of the laser beamapplication position is carried out as described above, the chuck table41 is moved to a laser beam application area where the condenser 424 ofthe laser beam application means 42 for applying a laser beam is locatedas shown in FIG. 6( a), so as to position one end (left end in FIG. 6(a)) of the predetermined dividing line 21 right below the condenser 424of the laser beam application means 42. The chuck table 41, that is, thesemiconductor wafer 2 is moved in the direction indicated by the arrowX1 in FIG. 6( a) at a predetermined feed rate while a pulse laser beamcapable of passing through the semiconductor wafer is applied from thecondenser 424. When the application position of the condenser 424 of thelaser beam application means 42 reaches the other end of the dividingline 21 as shown in FIG. 6( b), the application of the pulse laser beamis suspended and the movement of the chuck table 41, that is, thesemiconductor wafer 2 is stopped. In this deteriorated layer formingstep, by setting the focusing point P of the pulse laser beam to aposition near the back surface 2 b (undersurface) of the semiconductorwafer 2, a deteriorated layer 210 which is exposed to the back surface 2b (undersurface) is formed inward from the back surface 2 b. Thisdeteriorated layer 210 is formed as a molten-resolidified layer of whichthe wafer has been once molten and then re-solidified. By forming thedeteriorated layer 210 exposed to the back surface 2 b of thesemiconductor wafer 2, the semiconductor wafer 2 can be easily dividedby exerting external force along the deteriorated layers 210.

The processing conditions in the above deteriorated layer forming stepare set as follows, for example.

-   Light source: LD excited Q switch Nd: YVO4 laser-   Wavelength: pulse laser having a wavelength of 1,064 nm-   Pulse output: 10 μJ-   Focusing spot diameter: 1 μm-   Pulse width: 40 ns-   Peak power density of focusing point: 3.2×10¹⁰ W/cm²-   Repetition frequency: 100 kHz-   Processing-feed rate: 100 mm/sec.

When the semiconductor wafer 2 is large in thickness, as shown in FIG.7, the above-described deteriorated layer forming step is carried outseveral times by changing the focusing point P stepwise so as to form aplurality of deteriorated layers 210. Since the deteriorated layerformed once under the above processing conditions is as thick as about50 μm, six deteriorated layers are formed in the wafer 2 having athickness of 300 μm in the illustrated embodiment. As a result, thedeteriorated layers 210 formed in the inside of the semiconductor wafer2 extend from the back surface 2 b to the front surface 2 a along thedividing line 21.

The step of dividing the semiconductor wafer 2 along the dividing lines21 comes after the above deteriorated layer forming step.

A first example of the dividing step will be described with reference toFIG. 8. This first example of the dividing step shown in FIG. 8 iscarried out by using an ultrasonic dividing device 5. The ultrasonicdividing device 5 comprises a cylindrical base 51, a first ultrasonicgenerator 52 and a second ultrasonic generator 53. The cylindrical base51 constituting the ultrasonic dividing device 5 has, at its topsurface, a placing surface 51 a for placing the above frame 3 so thatthe frame 3 is placed thereon and fixed by clamps 54. This base 51 is soconstituted as to be able to be moved in a horizontal direction and adirection perpendicular to the sheet in FIG. 8 and to be turned by amoving means that is not shown. The first ultrasonic generator 52 andthe second ultrasonic generator 53 constituting the ultrasonic dividingdevice 5 are arranged at opposite positions above and below thesemiconductor wafer 2 supported on the frame 3 placed on the placingsurface 51 a of the cylindrical base 51 via the dicing tape 30 andgenerate longitudinal waves (compressional waves) having a predeterminedfrequency. To carry out the above dividing step by using the thusconstituted ultrasonic dividing device 5, the frame 3 supporting thesemiconductor wafer 2 (in which the deteriorated layers 210 are formedalong the dividing lines 21) via the dicing tape 30 is placed on theplacing surface 51 a of the cylindrical base 51 in such a manner thatthe dicing tape 30-placing side comes into contact with the placingsurface 51 a (therefore, the front surface 2 a of the semiconductorwafer 2 faces up) and fixed by the clamps 54. Thereafter, the base 51 isoperated by the moving means (not shown) to bring one end (left end inFIG. 8) of a predetermined dividing line 21 formed on the semiconductorwafer 2 to a position where ultrasonic waves from the first ultrasonicgenerator 52 and the second ultrasonic generator 53 can act thereon. Thefirst ultrasonic generator 52 and the second ultrasonic generator 53 arerespectively activated to generate longitudinal waves (compressionalwaves) having a frequency of, for example, 28 kHz while the base 51 ismoved in the direction indicated by the arrow at a feed rate of 50 to100 m/sec. As a result, ultrasonic waves from the first ultrasonicgenerator 52 and the second ultrasonic generator 53 act on the frontsurface and back surface of the semiconductor wafer 2 along the dividingline 21, whereby the semiconductor wafer 2 is divided along the dividingline 21 whose strength has been reduced by the formation of thedeteriorated layer 210. After the dividing step is thus carried outalong the predetermined dividing line 21, the base 51 is moved adistance corresponding to the interval between dividing lines 21 in theindexing direction perpendicular to the sheet to carry out the abovedividing step. After the dividing step is carried out along all thedividing lines 21 extending in the predetermined direction, the base 51is turned at 90° to further carry out the above dividing step alongdividing lines 21 formed on the semiconductor wafer 2 in a directionperpendicular to the predetermined direction, thereby dividing thesemiconductor wafer 2 into individual semiconductor chips. Since theback surfaces of the obtained chips have the dicing tape 30 affixedthereto, the chips do not fall apart and maintain the state of thewafer.

A second example of the dividing step will be described with referenceto FIG. 9. This second example of the dividing step shown in FIG. 9 iscarried out by using a laser beam processing machine similar to thelaser beam processing machine shown in FIGS. 3 to 5. That is, thesemiconductor wafer 2 (in which the deteriorated layers 210 are formedalong the dividing lines 21) supported to the frame 3 via the dicingtape 30 is placed on the chuck table 61 of the laser beam processingmachine 6 in such a manner that the dicing tape 3 side comes intocontact with the chuck table 61 (therefore, the front surface 2 a of thesemiconductor wafer 2 faces up) and suction-held by a suction means thatis not shown, and the frame 3 is fixed by a clamp mechanism 62.Thereafter, the chuck table 61 is moved to a laser beam application areawhere the condenser 63 of laser beam application means is located tobring one end (left end in FIG. 9) of a predetermined dividing line 21to a position right below the condenser 63. The chuck table 61, that is,the semiconductor wafer 2 is moved in the direction indicated by thearrow X1 in FIG. 9 at a predetermined feed rate while a continuous-wavelaser beam having absorptivity for the semiconductor wafer 2 is appliedfrom the condenser 63. When the application position of the condenser 63reaches the other end (right end in FIG. 9) of the predetermineddividing line 21, the application of the laser beam is suspended and themovement of the chuck table 61, that is, the semiconductor wafer 2 isstopped. In this dividing step, by setting the focusing point P of thecontinuous-wave laser beam to the front surface 2 a (top surface) of thesemiconductor wafer 2 to heat the dividing line 21 where thedeteriorated layer 210 has been formed, thermal stress is generated,thereby giving a heat shock. As a result, a split portion is formedalong the dividing line 21 where the deteriorated layer 210 has beenformed to divide the semiconductor wafer 2. The output of the laser beamapplied along the dividing line 21 where the deteriorated layer 210 hasbeen formed in the dividing step is enough to heat the semiconductorwafer 2 to such an extent that it gives a moderate temperature gradient(100 to 400° C.), and such temperature does not melt silicon.

The processing conditions in the above dividing step are set as follows,for example.

-   Light source: LD excited Nd: YAG second harmonic laser (CW)-   Wavelength: 532 nm-   output: 10 W-   Focusing spot diameter: 0.5 mm (heating a relatively wide area    including the deteriorated layer 210)-   Processing-feed rate: 100 mm/sec

After the above dividing step is carried out, the chuck table 61, thatis, the semiconductor wafer 2 is moved a distance corresponding to theinterval between dividing lines 21 in the indexing directionperpendicular to the sheet in FIG. 9 while a continuous-wave laser beamis applied as described above. After the above processing-feeding andindex-feeding are carried out along all the dividing lines 21 formed inthe predetermined direction, the chuck table 61, that is, thesemiconductor wafer 2 is turned at 90° to carry out the aboveprocessing-feed and indexing-feed along dividing lines 21 formed in adirection perpendicular to the above predetermined direction, wherebythe semiconductor wafer 2 is split and divided along the dividing lines21. Although the semiconductor wafer 2 is split along the dividing lines21 to be divided into individual chips, the individual chips do not fallapart and maintain the state of the wafer as the back surface 2 b of thesemiconductor wafer 2 has the dicing tape 30 affixed thereto.

A third example of the dividing step will be described with reference toFIG. 10. This third example of the dividing step shown in FIG. 10 iscarried out by using a bending dividing device 7, which comprises acylindrical base 71 and a bending load application means 73. That is,the frame 3 supporting the semiconductor wafer 2 (in which thedeteriorated layers 210 are formed along the dividing lines 21) via thedicing tape 30 is placed on the placing surface 71 a of the cylindricalbase 71 in such a manner that the dicing tape 30 side faces up(therefore, the front surface 2 a of the semiconductor wafer 2 facesdown) and fixed by clamps 72. The front surface 2 a (undersurface) ofthe semiconductor wafer 2 is then placed on a plurality of columnarsupport members 74 that are arranged parallel to one another andconstitute the bending load application means 73. At this point, thesemiconductor wafer 2 is placed in such a manner that each dividing line21 formed in a predetermined direction of the semiconductor wafer 2 ispositioned between adjacent support members 74 and 74. The semiconductorwafer 2 is then pressed by pressing members 75 along the dividing lines21 from the side of the dicing tape 30 affixed to the back surface 2 bof the semiconductor wafer 2. As a result, a bending load acts on thesemiconductor wafer 2 along the dividing lines 21 to generate tensilestress on the front surface 2 a, whereby the semiconductor wafer 2 issplit and divided along the dividing lines 21 whose strength has beenreduced by the formation of the deteriorated layers 210. After thesemiconductor wafer 2 is divided along the deteriorated layers 210, thatis, the dividing lines 21 formed in the predetermined direction, thecylindrical base 71, that is, the semiconductor wafer 2 is turned at 90°and the above dividing work is carried out along dividing lines 21formed in a direction perpendicular to the above predetermined directionto divide the semiconductor wafer 2 into individual chips. Since theback surfaces of the individual chips have the dicing tape 30 affixedthereto, the chips do not fall apart and maintain the state of thesemiconductor wafer 2.

A fourth example of the dividing step will be described with referenceto FIG. 11. This fourth example of the dividing step shown in FIG. 11 iscarried out by using a bending dividing device 8, which comprises acylindrical base 81 and a pressing member 83 as a bending loadapplication means. This base 81 is so constituted as to be able to bemoved in the horizontal direction and the direction perpendicular to thesheet in FIG. 11 and also turned by a moving means that is not shown.The frame 3 supporting the semiconductor wafer 2 (in which thedeteriorated layers 210 are formed along the dividing lines 21) via thedicing tape 30 is placed on the placing surface 81 a of the thusconstituted cylindrical base 81 in such a manner that the dicing tape 30side comes into contact with the placing surface 81 a (therefore, thefront surface 2 a of the semiconductor wafer 2 faces up) and fixed byclamps 82. Thereafter, the base 81 is operated by the moving means (notshown) to bring one end (left end in FIG. 11) of a predetermineddividing line 21 formed on the semiconductor wafer 2 to a positionopposite to the pressing member 83, and the pressing member 83 is movedup in FIG. 11 to a position where it presses the dicing tape 30 affixedto the semiconductor wafer 2. The base 81 is moved in the directionindicated by the arrow. As a result, a bending load is applied to thesemiconductor wafer 2 along the dividing line 21 pressed by the pressingmember 83 to generate tensile stress on the front surface 2 a, wherebythe semiconductor wafer 2 is split and divided along the dividing line21 whose strength has been reduced by the formation of the deterioratedlayer 210. After the dividing step is carried out along thepredetermined dividing line 21, the base 81 is moved a distancecorresponding to the interval between dividing lines 21 in the indexingdirection perpendicular to the sheet to carry out the above dividingstep. After the dividing step is carried out on all the dividing lines21 extending in the predetermined direction, the base 81 is turned at90° to carry out the above dividing step on dividing lines 21 formed ina direction perpendicular to the predetermined direction, therebydividing the semiconductor wafer 2 into individual chips. Since the backsurfaces of the obtained chips have the dicing tape 30 affixed thereto,the chips do not fall apart and maintain the state of the wafer.

In the step of dividing the semiconductor wafer 2 along the dividinglines 21, for example, a method of splitting the semiconductor wafer 2along the dividing lines 21 whose strength has been reduced by theformation of the deteriorated layers 210 by placing the semiconductorwafer 2 having the dicing tape 30 affixed thereto on a soft rubber sheetand pressing the top surface of the semiconductor wafer 2 with a rollermay be employed, besides the above-described dividing method.

After the above dividing step is carried out, there comes an expansionstep for enlarging the interval between chips by stretching the dicingtape 30 affixed to the wafer divided into individual chips. Thisexpansion step is carried out by using a pick-up device 9 shown in FIG.12 and FIGS. 13( a) and 13(b). The pick-up device 9 will be describedhereinbelow. The illustrated pick-up device 9 comprises a cylindricalbase 91 having a placing surface 91 a for placing the above frame 3 andan expanding means 92 for stretching the dicing tape 30 mounted to theframe 3 and arranged in the base 91 concentrically. The expanding means92 comprises a stretching member 93 for supporting the area 301 wherethe semiconductor wafer 2 exists in the dicing tape 30. This stretchingmember 93 can move vertically (axial direction of the cylindrical base91) between a standard position shown in FIG. 13( a) and an expansionposition shown in FIG. 13( b) above the standard position by a liftingmeans that is not shown. In the illustrated embodiment, ultravioletlamps 94 are installed in the stretching member 93.

The expansion step which is carried out using the above pick-up device 9will be described with reference to FIG. 12 and FIGS. 13( a) and 13(b).

The frame 3 mounting the dicing tape 30 affixed to the back surface 2 bof the semiconductor wafer 2 divided into individual chips 20 asdescribed above is placed on the placing surface 91 a of the cylindricalbase 91 and fixed on the base 91 by clamps 95 as shown in FIG. 12 andFIG. 13( a). Then, the stretching member 93 of the expanding means 92supporting the area 301 where the wafer 2 exists in the above dicingtape 30 is moved up to the expansion position shown in FIG. 13( b) fromthe standard position shown in FIG. 13( a) by the lifting means that isnot shown. As a result, the extensible dicing tape 30 is stretched,whereby a slippage occurs between the dicing tape 30 and the chips 20,thereby reducing adhesion therebetween. Therefore, the chips 20 can beeasily picked up from the dicing tape 30, and a space is formed betweenadjacent semiconductor chips 20.

Then, a pick-up collet 96 arranged above the pick-up device 9 isactivated to pick up the individual chips 20 from the upper surface ofthe dicing tape 30 and carry them to a tray (not shown), as shown inFIG. 12 (pick-up step). At this point, the ultraviolet lamps 94 in thestretching member 93 are turned on to apply ultraviolet radiation to thedicing tape 30 so as to reduce the adhesive strength of the dicing tape30, thereby making it possible to pick up the semiconductor chips 20from the dicing tape 30 more easily.

The above dividing step may also be carried out by using the abovepick-up device 9. That is, as shown in FIG. 14( a), the frame 3supporting the semiconductor wafer 2 (in which the deteriorated layers210 are formed along the dividing lines 21) via the dicing tape 30before the above dividing step is carried out is placed on the placingsurface 91 a of the cylindrical base 91 and fixed on the base 91 by theclamps 95. As shown in FIG. 14( b), the stretching member 93 of theexpanding means 92 supporting the area 301 where the wafer 2 exists inthe above dicing tape 30 is moved up from the standard position shown inFIG. 14( a) to the expansion position shown in FIG. 14( b) by thelifting means that is not shown. As a result, the extensible dicing tape30 is stretched so that tensile force acts radially on the semiconductorwafer 2 having the dicing tape 30 affixed thereto. When tensile forcethus acts radially on the semiconductor wafer 2, the semiconductor wafer2 is split along the deteriorated layers 210 to be divided intoindividual semiconductor chips 20 as the strength of the deterioratedlayers 210 formed along the dividing lines 21 has been reduced. Theexpansion or elongation of the dicing tape 30 in the above dividing stepcan be adjusted by the upward movement of the stretching member 93.According to experiments conducted by the inventors of the presentinvention, when the dicing tape 30 was stretched about 20 mm, thesemiconductor wafer 2 could be divided along the deteriorated layers210. By carrying out the dividing step like this, a slippage occursbetween the dicing tape 30 and the chips 20, thereby reducing adhesiontherebetween. As a result, the chips 20 can be easily picked up from thedicing tape 30 and a space is formed between adjacent chips 20.Thereafter, the pick-up collet 96 arranged above the pick-up device 9 isactivated to pick up the individual chips 20 from the dicing tape 30 andcarry them to the tray (not shown), as shown in FIG. 12.

1. A method of dividing, a wafer having function elements formed inareas sectioned by a plurality of dividing lines formed in a latticepattern on the front surface, comprising: a frame holding step foraffixing the back surface of the wafer to a dicing tape mounted on anannular frame; a deteriorated region forming step for forming aplurality of deteriorated regions along the plurality of dividing linesin the inside of the wafer by applying a pulse laser beam, capable ofpassing through the wafer, to the wafer along the plurality of dividinglines, from the side of the front surface of the wafer held on theframe; a dividing step for dividing the wafer into individual chipsalong the plurality of dividing lines by exerting external force alongthe plurality of dividing lines where the plurality of deterioratedregions have been formed in the wafer held on the frame; an expansionstep for enlarging the interval between chips by stretching the dicingtape affixed to the wafer divided into individual chips; and a pickingup step for picking up each chip from the expanded dicing tape.
 2. Thewafer dividing method according to claim 1, wherein the plurality ofdeteriorated regions formed in the inside of the wafer in thedeteriorated region forming step are exposed to at least the backsurface of the wafer.
 3. The wafer dividing method according to claim 1,wherein the dividing step is carried out by stretching the dicing tapein the expansion step.